Electrode manufacturing method

Abstract

This electrode includes a core material, and an electrode mixture laminated on the surface of the core material. The electrode mixture contains an active material, a conductive material, and a fibrous binding material, wherein the ratio of the density of the electrode mixture to the true density of the active material is at least 72%, and the maximum infiltration depth of the active material in the core material is at most 18% of the thickness of the core material.

Description

[Technical Field]

[0001] This disclosure , electric This relates to a method for manufacturing a pole. [Background technology]

[0002] Electrodes for nonaqueous electrolyte secondary batteries such as lithium-ion batteries are generally produced by a wet method in which an electrode mixture slurry containing an active material, a binder, and the like is applied to the surface of a metal foil core material, and the resulting coating is then dried and compressed. This method presents a problem of the tendency for the binder to migrate during drying. When binder migration occurs, the amount of binder is greater on the surface side of the coating film (electrode mixture layer) than on the core material side, resulting in a bias in the distribution of the binder in the thickness direction of the electrode mixture layer.

[0003] In recent years, a dry method has been studied in which an electrode mixture is rolled into a sheet to produce an electrode mixture sheet, and the sheet is then attached to a core material to produce an electrode. Patent Document 1 discloses an electrode film (electrode mixture) produced by mixing an active material, a particulate binder, and a conductive material using a mill, and then treating the mixture under high pressure and large shearing force for a long period of time to fibrillate the binder. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2019-512872 Summary of the Invention

[0005] To improve battery characteristics, it is necessary to increase the density of the electrode mixture. As a result of investigations by the present inventors, it was found that, although the density of the electrode mixture can be increased by increasing the linear pressure when laminating the electrode mixture sheet disclosed in Patent Document 1 to the core material, the active material is deeply embedded in the core material, resulting in a decrease in the strength of the core material. The technology disclosed in Patent Document 1 does not consider achieving both an increase in the density of the electrode mixture and suppression of a decrease in the strength of the core material, and there is still room for improvement.

[0006] An electrode according to one embodiment of the present disclosure includes a core material and an electrode composite laminated on the surface of the core material. The electrode composite includes an active material, a conductive material, and a fibrous binder, and the ratio of the density of the electrode composite to the true density of the active material is 72% or more, and the maximum penetration depth of the active material into the core material is 18% or less of the thickness of the core material.

[0007] An electrode manufacturing method according to one embodiment of the present disclosure is the above-described electrode manufacturing method, and includes a mixing step of mixing a powdered active material, a powdered conductive material, and a powdered fibrous binder to produce electrode composite particles having a solid content of substantially 100%, a rolling step of rolling the electrode composite particles to form them into a sheet to produce an electrode composite sheet, a compression step of compressing the electrode composite sheet to produce a high-density electrode composite sheet, and a lamination step of laminating the high-density electrode composite sheet to a core material to produce an electrode.

[0008] According to one aspect of the present disclosure, it is possible to achieve both high density of the electrode mixture and suppression of a decrease in the strength of the core material. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view of an electrode according to an embodiment. [Figure 2] FIG. 2 is a schematic diagram showing the active material in the cross section of FIG. 1, enlarging the vicinity of the core material. [Figure 3] FIG. 3(a) is a diagram showing a mixing step, and FIG. 3(b) is a diagram showing a rolling step in a manufacturing process of an electrode according to an embodiment. [Figure 4] FIG. 4 is a diagram showing a compression step in the manufacturing process of an electrode according to an embodiment. [Figure 5] FIG. 5 is a diagram showing a bonding step in the manufacturing process of an electrode according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of an electrode and an electrode manufacturing method according to the present disclosure will be described in detail. The embodiments described below are merely examples, and the present disclosure is not limited to the following embodiments. Furthermore, the drawings referred to in the description of the embodiments are schematic, and the dimensional ratios of the components depicted in the drawings should be determined in consideration of the following description.

[0011] [electrode] The electrode according to the present disclosure is suitable for non-aqueous electrolyte secondary batteries such as lithium ion batteries, but can also be applied to batteries containing aqueous electrolytes or power storage devices such as capacitors. The following description will be given taking as an example an electrode for a non-aqueous electrolyte secondary battery (particularly when applied to a positive electrode).

[0012] FIG. 1 is a cross-sectional view of an electrode according to an embodiment. Electrode 10 includes a core material 11 and an electrode composite material 12 laminated on the surface of core material 11. As shown in FIG. 1, electrode 10 may include electrode composite material 12 on both sides of core material 11. Electrode 10 may be a long electrode constituting a wound electrode body, or a rectangular electrode constituting a laminated electrode body. Electrode 10 may be used as a positive electrode, a negative electrode, or both of a nonaqueous electrolyte secondary battery.

[0013] The core material 11 may be a metal foil or a film with a metal layer formed on its surface. The thickness of the core material 11 is, for example, 5 μm to 20 μm. In the case of a positive electrode, the core material 11 may be a metal foil containing aluminum as its main component. In the case of a negative electrode, the core material 11 may be a metal foil containing copper as its main component. In this specification, the term "main component" refers to the component with the highest mass ratio. The core material 11 may be an aluminum foil that is substantially 100% aluminum, or a copper foil that is substantially 100% copper.

[0014] The electrode mixture 12 includes an active material, a conductive material, and a fibrous binder. The active material, conductive material, and fibrous binder may be in a powder state. The thickness of the electrode mixture 12 is, for example, 30 μm to 120 μm, and preferably 50 μm to 100 μm. Examples of conductive materials contained in the electrode mixture 12 include carbon materials such as carbon black (CB), acetylene black (AB), ketjen black, carbon nanotubes (CNT), and graphite. The particle diameter of the conductive material is, for example, 0.01 μm to 0.1 μm. This allows the conductive material to penetrate and adhere to recesses on the surface of the positive electrode active material. The content of the conductive material in the electrode mixture 12 can be, for example, 0.5% by mass to 5.0% by mass.

[0015] Lithium transition metal composite oxides are generally used for the positive electrode active material (positive electrode active material). Metal elements contained in the lithium transition metal composite oxides include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. Among these, at least one of Ni, Co, and Mn is preferably contained. Carbon-based active materials, such as natural graphite (e.g., flake graphite, lump graphite, and amorphous graphite), and artificial graphite (e.g., massive artificial graphite (MAG) and graphitized mesophase carbon microbeads (MCMB)), are used for the negative electrode active material. Alternatively, Si-based active materials that can be alloyed with lithium may be used for the negative electrode active material. The active material is the main component of the electrode mixture 12, and the content of the active material in the electrode mixture 12 is preferably 85% to 99% by mass, and more preferably 90% to 99% by mass.

[0016] The positive electrode active material is, for example, a secondary particle formed by agglomeration of a plurality of primary particles. As a result, irregularities exist on the surface of the positive electrode active material, and as described above, the conductive material can penetrate and adhere to the recesses of the irregularities. The particle size of the primary particles constituting the secondary particles is, for example, 0.05 μm to 1 μm. The particle size of the primary particles is measured as the diameter of the circumscribed circle in a particle image observed with a scanning electron microscope (SEM).

[0017] The average particle size of the active material is, for example, in the range of 1 μm to 40 μm. Here, the average particle size is the volume-based median diameter (D50). D50 refers to the particle size at which the cumulative frequency of the smallest particle size in the volume-based particle size distribution is 50%, and is also called the median diameter. The particle size distribution of the active material can be measured using a laser diffraction particle size distribution analyzer (e.g., MT3000II manufactured by Microtrack-Bell Corporation) with water as the dispersion medium. When there is one type of active material, i.e., when the particle size distribution of the active material has one peak, the average particle size is preferably in the range of 1 μm to 20 μm, more preferably in the range of 5 μm to 15 μm.

[0018] The active material may include a first active material and a second active material. Preferably, the first active material has an average particle size in the range of 3 μm to 7 μm, and the second active material has an average particle size in the range of 10 μm to 34 μm. By including a first active material and a second active material with different average particle sizes, the packing rate of the active material increases, and the density of the electrode mixture can be increased.

[0019] The mixing ratio of the first active material to the second active material is preferably in the range of 10:90 to 30:70 by mass, which allows the electrode mixture to have a higher density.

[0020] The first active material and the second active material may have the same composition. The first active material and the second active material may be positive electrode active materials or may be NCA-based (Ni-Co-Al-based) lithium transition metal composite oxides. The active material may contain an active material other than the first active material and the second active material.

[0021] The fibrous binder is, for example, fibrillated PTFE. The fibrous binder is a powder in a dry state, not a powder dispersed in a dispersion such as water. This allows the electrode mixture to be produced by a dry process described below. Note that the electrode mixture 12 may contain, in addition to the fibrous binder, a binder such as non-fibrillated polyvinylidene fluoride (PVdF).

[0022] The content of the fibrous binder in the electrode mixture 12 is, for example, 0.5% by mass to 5.0% by mass. The fibrous binder adheres to the particle surfaces of the active material and is entangled with the active material. In other words, the active material is held in place by the fibrous binder present in a network shape.

[0023] The fibrous binder can be produced by fibrillating a PTFE raw material (PTFE particles) that belongs to the fibrillable fine powder category using a dry grinder such as a jet mill grinder. The PTFE raw material may be secondary particles. The particle diameter of the PTFE raw material is, for example, 100 μm to 700 μm, preferably 100 μm to 500 μm, and more preferably 100 μm to 400 μm. The particle diameter of the PTFE raw material can be determined by observing the particles of the PTFE raw material using an SEM. Specifically, the external shapes of 100 randomly selected particles are identified, and the major axis (longest diameter) of each of the 100 particles is determined, and the average value thereof is taken as the particle diameter of the PTFE raw material.

[0024] The median diameter (D50) of the fibrous binder is preferably 2 μm to 20 μm. A median diameter of the fibrous binder of 2 μm to 20 μm means that the fibrous binder has a size that is finer than the PTFE particles of the PTFE raw material.

[0025] When the electrode mixture 12 is divided into three equal parts in the thickness direction, namely, a first region, a second region, and a third region from the core material 11 side, the content of the fibrous binder in the first region (a), the content of the fibrous binder in the second region (b), and the content of the fibrous binder in the third region (c) preferably satisfy (ca) / (a+b+c)≦±10%, and more preferably satisfy (ca) / (a+b+c)≦±5%. This allows the fibrous binder to be present substantially uniformly throughout the electrode mixture 12, rather than being present only in a portion of the electrode mixture 12. By using the dry process described below, the fibrous binder can be present substantially uniformly throughout the electrode mixture 12.

[0026] The electrode 10 may further include an adhesive layer between the core material 11 and the electrode mixture 12. The thickness of the adhesive layer is, for example, 1 μm to 10 μm. The adhesive layer has a function of bonding the core material 11 and the electrode mixture 12 together, thereby improving the adhesion between the core material 11 and the electrode mixture 12. The adhesive layer may also be conductive. The adhesive layer includes, for example, a conductive material and a binder. Examples of conductive materials included in the adhesive layer include carbon materials such as carbon black (CB), acetylene black (AB), ketjen black, carbon nanotubes (CNT), and graphite. The conductive material preferably has a small particle diameter and a large specific surface area. This makes it easier for the adhesive layer to form a structure. The specific surface area of ​​the conductive material is, for example, 100 m 2 / g~150m 2 / g range. Examples of binders contained in the adhesive layer include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide, acrylic resin, and polyolefin. PVdF is preferred as the binder contained in the adhesive layer. The adhesive layer can be produced, for example, by applying a slurry containing a conductive material, a binder, and the like to the surface of the core material 11, drying the coating, and then compressing it. The adhesive layer can also be produced on the surface of the core material 11 by dip coating or spray coating.

[0027] The content of the conductive material in the adhesive layer is preferably 40% by mass to 80% by mass, more preferably 45% by mass to 75% by mass, and particularly preferably 50% by mass to 71% by mass. By making the content of the conductive material in the adhesive layer relatively large in this way, it is possible to reduce the interfacial resistance. If the amount of conductive material is too large, the strength of the adhesive layer itself decreases and the layer structure becomes brittle, thereby inhibiting conductivity between the electrode mixture 12 and the core material 11. From the viewpoint of improving battery characteristics, the interfacial resistance of the electrode 10 should be 0.12 Ωcm. 2 It is preferable that the interface resistance is as follows: The interface resistance can be measured using, for example, an electrode resistance measuring device (device name: XF057) manufactured by Hioki E.E. Corporation.

[0028] Next, the state in the vicinity of the core material 11 will be described with reference to Fig. 2. Fig. 2 schematically illustrates the vicinity of the core material 11 while showing the active material 14. As shown in Fig. 2, a portion of the active material 14 is embedded in the core material 11. The embedding of the active material 14 in the core material 11 can improve the adhesion between the electrode mixture 12 and the core material 11.

[0029] The maximum penetration ratio (P / T), defined as the ratio of the maximum penetration depth P of the active material 14 into the core material 11 to the thickness T of the core material 11, is 18% or less. P / T is preferably 15% or less, more preferably 10% or less, and particularly preferably 8% or less. This makes it possible to improve the adhesion between the electrode mixture 12 and the core material 11 while ensuring the strength of the core material 11. Furthermore, P / T is preferably 1% or more, more preferably 3% or more, and particularly preferably 5% or more.

[0030] The maximum penetration depth P can be determined by observing the cross section of the electrode 10 with an SEM, as shown in FIG. 2. More specifically, when the cross section of the electrode 10 is magnified 1500 times with an SEM and five or more active material particles 14 are observed to have penetrated into the core material 11, the maximum penetration depths of any five active material particles 14 are determined, and the average of these is defined as the maximum penetration depth P. When the cross section of the electrode 10 is magnified 1500 times with an SEM and there are fewer than five active material particles 14 that have penetrated into the core material 11, the maximum penetration depth is determined for each active material particle 14, and the average of these is defined as the maximum penetration depth P. In the example of FIG. 2, four active material particles 14 have penetrated into the core material 11, so the maximum penetration depth is determined for each of the penetrated active material particles 14, and the average of these is defined as P.

[0031] The ratio (Dm / Dt) of the density Dm of the active material 14 in the electrode mixture 12 to the true density Dt of the active material 14 is 72% or more. Furthermore, Dm / Dt is preferably 74% or more. When Dm / Dt is 72% or more, it can be said that the filling rate of the active material in a given mixture volume is high. The density Dm of the active material 14 in the electrode mixture 12 can be calculated by multiplying the electrode mixture density, calculated by dividing the mass of the electrode mixture 12 by the volume of the electrode mixture 12, by the mass ratio of the active material 14 in the electrode mixture.

[0032] [Electrode manufacturing method] The method for manufacturing the electrode 10 will be described in more detail below. While the method for manufacturing a positive electrode will be exemplified below, this manufacturing method can also be applied to the manufacture of a negative electrode. In the case of a negative electrode, a negative electrode active material is used instead of a positive electrode active material.

[0033] 3, 4, and 5 are diagrams schematically illustrating the manufacturing process of an electrode 10 according to an embodiment. The manufacturing method of the electrode 10 includes a mixing step shown in FIG. 3(a), a rolling step shown in FIG. 3(b), a compression step shown in FIG. 4, and a laminating step shown in FIG. 5. In the mixing step, an active material and a fibrous binder are mixed to produce electrode mixture particles 12a having a solid content of substantially 100%. In the rolling step, the electrode mixture particles 12a are rolled and formed into a sheet to produce an electrode mixture sheet 12b. In the compression step, the electrode mixture sheet 12b is compressed to produce a high-density electrode mixture sheet 12c. In the laminating step, the high-density electrode mixture sheet 12c is laminated to a core material 11 to produce an electrode.

[0034] The method for manufacturing electrode 10 is a dry process for manufacturing electrode 10 using electrode mixture 12 having a solid content concentration of substantially 100%. The dry process is a process in which active material particles and binder particles are mixed without using a solvent, that is, the active material and binder are mixed in a state in which the solid content concentration of the active material and binder is substantially 100%. The method for manufacturing electrode 10 according to the present disclosure does not require the use of a solvent as in conventional methods for manufacturing electrode 10. Not requiring the use of a solvent not only means that a solvent is not required as a raw material, but also means that a solvent drying process is not required, and exhaust equipment and the like related to the drying process are also not required.

[0035] In the mixing step, raw materials such as an active material, a fibrous binder, and a conductive material are mixed in a mixer 20 to produce electrode composite particles 12a. For example, a conventional mechanical agitation mixer can be used as the mixer 20. Specific examples of suitable mixers 20 include devices capable of applying mechanical shearing force, such as cutter mills, pin mills, bead mills, microparticle composite devices (devices in which shearing force is generated between a specially shaped rotor rotating at high speed inside a tank and an impact plate), granulators, and kneaders such as twin-screw extrusion mixers and planetary mixers. Cutter mills, microparticle composite devices, granulators, and twin-screw extrusion mixers are preferred. This allows the fibrous binder to be further fibrillated while mixing the raw materials. The processing time for the mixing step (the time during which shearing force is applied to the materials) is preferably within a few minutes, e.g., 0.5 to 10 minutes. If the processing time is too long, the amount of conductive material incorporated into the fibrous binder increases. In this case, the conductivity of the electrode mixture sheet is significantly reduced, and the resistance increases, adversely affecting the battery characteristics.

[0036] The mixing step may include a step of mixing an active material and a conductive material to prepare a coated active material, and a step of mixing the coated active material and a fibrous binder. By using a coated active material prepared by mixing an active material and a conductive material, the time required to mix the coated active material and the fibrous binder can be shortened. This reduces the amount of conductive material incorporated into the fibrous binder. It is preferable that the surface of the coated active material has irregularities, and that the conductive material penetrates and adheres to the recesses in the irregularities. This makes it less likely that the conductive material on the surface of the coated active material will be taken up by the fibrous binder during the mixing process of the coated active material and the fibrous binder.

[0037] Mechanofusion, for example, may be used as a method for dry-mixing the active material and conductive material. Mechanofusion is a dry processing method carried out in a mechanofusion reactor, which has a cylindrical chamber equipped with a compression tool and rotates at high speed. The conductive material and active material are placed in the chamber, and by rotating the chamber, the particles are pressed against each other and against the chamber wall. The use of a compression tool and the generation of centrifugal force by high-speed rotation promotes adhesion and bonding between the conductive material and the active material. Examples of mechanofusion reactors include the "Nobilta" (registered trademark) or "Mechanofusion" (registered trademark) pulverizers manufactured by Hosokawa Micron Corporation (Japan), the "Hybridizer" (trademark) pulverizer manufactured by Nara Machinery Works, Ltd., the "Balance Gran" manufactured by Freund-Turbo Corporation, and the "COMPOSI" manufactured by Nippon Coke & Engineering Co., Ltd.

[0038] Next, in the rolling step, as shown in FIG. 3(b), the electrode mixture particles 12a are rolled using two rolls 22 to form a sheet. The two rolls 22 are arranged with a predetermined gap between them and rotate in the same direction. The electrode mixture particles 12a are supplied to the gap between the two rolls 22, whereby they are compressed by the two rolls 22 and stretched into a sheet. The two rolls 22 have, for example, the same roll diameter. The obtained electrode mixture sheet 12b may be passed through the gap between the two rolls 22 multiple times, or may be stretched one or more times using other rolls with different roll diameters, peripheral speeds, gaps, etc. Alternatively, the rolls may be heated to heat-press the electrode mixture particles 12a.

[0039] The thickness of the electrode mixture sheet 12b can be controlled by, for example, the gap between the two rolls 22, the peripheral speed, the number of times of stretching, etc. In the rolling step, the electrode mixture particles 12a are preferably formed into a sheet using two rolls 22 with a peripheral speed ratio that differs by two times or more. By making the peripheral speed ratio of the two rolls 22 different, for example, it becomes easier to thin the electrode mixture sheet 12b, improving productivity.

[0040] Next, in the compression step, as shown in FIG. 4, the electrode mixture sheet 12b is compressed using two rolls 24 to produce a high-density electrode mixture sheet 12c. The two rolls 24, for example, have the same roll diameter, are arranged with a predetermined gap between them, and rotate in the same direction at the same peripheral speed. The two rolls 24 may apply a linear pressure of, for example, 1 t / cm to 5 t / cm. When a single type of active material is used, Dm / Dt can be 72% or more by compressing with a relatively high linear pressure of, for example, 3 t / cm to 5 t / cm. When the active material includes a first active material and a second active material, Dm / Dt can be 72% or more even when compressed with a relatively low linear pressure of, for example, 1 t / cm to 3 t / cm. The temperature of the two rolls 24 is not particularly limited and may be, for example, room temperature. The active material density of the high-density electrode mixture sheet 12c is, for example, 3.6 g / cm. 3 ~4.0g / cm 3 is.

[0041] Next, in the lamination step, as shown in Fig. 5, the high-density electrode mixture sheet 12c is laminated to the core material 11, thereby obtaining an electrode 10 in which a mixture layer made of the electrode mixture 12 is provided on the surface of the core material 11. Although Fig. 5 shows a state in which the electrode mixture 12 is bonded to only one surface of the core material 11, it is preferable that the electrode mixture 12 is bonded to both surfaces of the core material 11. Two sheets of the electrode mixture 12 may be bonded to both surfaces of the core material 11 at the same time, or one sheet may be bonded to one surface of the core material 11 and then the other sheet may be bonded to the other surface.

[0042] In the laminating step, two rolls 26 are used to laminate the high-density electrode mixture sheet 12c onto the surface of the core material 11. The two rolls 26 have, for example, the same roll diameter, are arranged with a predetermined gap between them, and rotate in the same direction at the same peripheral speed. The temperature of the two rolls 26 is, for example, 50°C to 300°C. The linear pressure applied by the two rolls 26 is preferably 0.1 t / cm to 2 t / cm, and more preferably 0.2 t / cm to 1 t / cm.

[0043] <Example> The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0044] Example 1 [Preparation of positive electrode composite particles (mixing step)] The first active material was an NCA-based (Ni-Co-Al-based) lithium transition metal composite oxide with an average particle size (D50) of 6.5 μm. Using a NOB300 Nobilta (registered trademark) manufactured by Hosokawa Micron Corporation, 1000 g of the lithium transition metal composite oxide and 10 g of carbon black (CB) were mixed for 5 minutes in a Nobilta pulverizer to prepare a carbon-coated first active material. The second active material was a lithium transition metal composite oxide with an average particle size (D50) of 21 μm and the same composition as the first active material. The carbon-coated second active material was prepared in the same manner as the first active material.

[0045] Next, the carbon-coated first active material and the carbon-coated second active material were mixed in a mass ratio of 20:80 to prepare a carbon-coated positive electrode active material. This carbon-coated positive electrode active material and a fibrous binder were placed in a mixer (Osaka Chemical, Wonder Crusher) in a mass ratio of 101:4 and mixed for 5 minutes at room temperature at a rotation speed of 5. The rotation speed of the Wonder Crusher was 28,000 rpm, the maximum rotation speed at 10. This mixing process yielded positive electrode mixture particles in which the carbon-coated positive electrode active material and the fibrous binder were uniformly dispersed. The resulting positive electrode mixture had a solids concentration of 100%.

[0046] [Preparation of positive electrode composite sheet (rolling step)] The resulting positive electrode composite particles were rolled between two rolls to produce a positive electrode composite sheet. The peripheral speed ratio of the two rolls was set to 1:3, and the thickness of the positive electrode composite sheet was adjusted to 100 to 120 μm.

[0047] [Preparation of high-density positive electrode composite sheet (compression step)] The obtained positive electrode mixture sheet was passed between two rolls at room temperature and compressed (linear pressure: 2.0 t / cm) to produce a high-density positive electrode mixture sheet.

[0048] [Positive electrode fabrication (bonding step)] The high-density positive electrode composite sheets were placed on the front and back surfaces of a 14.4 μm-thick core material, and the laminate of the high-density positive electrode composite sheet and core material was pressed (linear pressure: 0.2 t / cm) using two rolls heated to 200° C. to obtain a positive electrode. The combined thickness of the core material and the positive electrode composite sheets placed on both sides of the core material was adjusted to 170 μm to 180 μm.

[0049] [Evaluation of maximum penetration ratio (P / T)] The maximum penetration ratio (P / T) was calculated by the method described above.

[0050] [Dm / Dt rating] The ratio (Dm / Dt) of the density Dm of the active material in the positive electrode mixture to the true density Dt of the positive electrode active material was calculated by the method described above.

[0051] <Example 2> A positive electrode was prepared and evaluated in the same manner as in Example 1, except that an NCA-based lithium transition metal composite oxide having an average particle size (D50) of 14.2 μm was used as the second active material in the mixing step. The composition of the second active material in Example 2 was the same as that of the second active material in Example 1.

[0052] Example 3 A positive electrode was produced and evaluated in the same manner as in Example 1, except that in the mixing step, the mixing ratio of the carbon-coated first active material and the carbon-coated second active material was changed to 30:70 in mass ratio.

[0053] Example 4 A positive electrode was produced and evaluated in the same manner as in Example 1, except that in the mixing step, the mixing ratio of the carbon-coated first active material and the carbon-coated second active material was changed to 10:90 in mass ratio.

[0054] <Example 5> A positive electrode was produced and evaluated in the same manner as in Example 1, except that in the laminating step, the linear pressure for pressing the laminate of the high-density positive electrode composite sheet and the core material was changed to 1.0 t / cm.

[0055] Example 6 In the mixing step, a carbon-coated positive electrode active material was prepared using only one type of NCA-based lithium transition metal composite oxide having a D50 of 11 μm as the active material, and in the compression step, the linear pressure when compressing the positive electrode composite sheet was changed to 4.4 t / cm. Except for this, a positive electrode was prepared and evaluated in the same manner as in Example 1. The composition of the active material in Example 6 is the same as that of the active material in Example 1.

[0056] <Comparative Example 1> A carbon-coated positive electrode active material was prepared using only one type of NCA-based lithium transition metal composite oxide with a D50 of 11 μm as the active material in the mixing step, and a positive electrode was prepared and evaluated in the same manner as in Example 1, except that the compression step was not performed and the positive electrode composite sheet was attached to the core material under a linear pressure of 2.0 t / cm in the laminating step. The composition of the active material in Comparative Example 1 was the same as that of the active material in Example 1.

[0057] <Comparative Example 2> A positive electrode was produced and evaluated in the same manner as in Example 1, except that the compression step was not performed and the positive electrode composite sheet was attached to the core material under a linear pressure of 2.0 t / cm in the attachment step.

[0058] The evaluation results (P / T, Dm / Dt) of the examples and comparative examples are shown in Table 1. Table 1 also shows the average particle diameter (D50) of the first active material and the second active material, the mixing ratio of the first active material and the second active material, the roll temperature and linear pressure in the compression step, the roll temperature and linear pressure in the lamination step, and (ca) / (a+b+c).

[0059] [Table 1]

[0060] As shown in Table 1, the positive electrodes of the examples are able to suppress a decrease in the strength of the core material while increasing the density of the positive electrode composite. On the other hand, the positive electrodes of the comparative examples, which did not undergo the compression step, require a high linear pressure in the lamination step to increase the density of the positive electrode composite, resulting in a large P / T and an inability to ensure the strength of the core material. [Explanation of symbols]

[0061] 10 electrodes 11 Core material 12 Electrode mixture 12a Electrode mixture particles 12b Electrode mixture sheet 12c High-density electrode composite sheet 14 Active material 20 Mixer 22, 24, 26 rolls

Claims

1. A method for manufacturing an electrode including a core material and an electrode mixture laminated on a surface of the core material, the electrode mixture includes an active material, a conductive material, and a fibrous binder; a ratio of the density of the active material in the electrode mixture to the true density of the active material is 72% or more; a maximum penetration depth of the active material into the core material is 1% or more and 18% or less of a thickness of the core material; a mixing step of mixing the powdered active material, the powdered conductive material, and the powdered fibrous binder to prepare electrode mixture particles having a solid content concentration of substantially 100%; a rolling step of rolling the electrode mixture particles to form them into a sheet, thereby producing an electrode mixture sheet; a compressing step of compressing the electrode mixture sheet to produce a high-density electrode mixture sheet; and a laminating step of laminating the high-density electrode mixture sheet to the core material to produce an electrode.

2. the active material includes a first active material and a second active material; the first active material has an average particle size in the range of 3 μm to 7 μm; The method for manufacturing an electrode according to claim 1, wherein the average particle size of the second active material is in the range of 10 μm to 34 μm.

3. 3. The method for manufacturing an electrode according to claim 2, wherein a mixing ratio of the first active material to the second active material is in a range of 10:90 to 30:70 by mass ratio.

4. The method for manufacturing an electrode according to claim 2 or 3, wherein the first active material and the second active material have the same composition.

5. 5. The method for manufacturing an electrode according to claim 1, wherein when the electrode mixture is divided into three equal parts in a thickness direction, which are a first region, a second region, and a third region from the core material side, the content (a) of the fibrous binder in the first region, the content (b) of the fibrous binder in the second region, and the content (c) of the fibrous binder in the third region satisfy −10%≦(c−a) / (a+b+c)≦10%.

6. an adhesive layer containing a binder and a conductive material is further included between the core material and the electrode mixture, The method for manufacturing an electrode according to any one of claims 1 to 5, wherein the content of the conductive material in the adhesive layer is 40% by mass to 80% by mass.

7. The mixing step comprises: mixing the active material and the conductive material to prepare a coated active material; The method for manufacturing an electrode according to claim 1 , further comprising the step of mixing the coated active material with the fibrous binder.

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